Timeline • 1903 - Maurice Arthus – Described a stereotypical Hypersensitivity response in rabbits following repeated intradermal injection of protein antigens – The response, characterized by Stephen Canfield, MD PhD local erythema, induration, Assistant Professor hemorrhage and necrosis Division of Pulmonary, Allergy became known as the “Arthus and Critical Care Medicine Reaction” Timeline Timeline • 1893 - Emil von Behring •1906 - Clemens von Pirquet and Bela Schick – Working with diphtheria toxin noted that animals would suffer –Coined the term “serum sickness” to describe strange systemic symptoms enhanced responses and even suffered by some patients weeks death following a second dose after receiving diphtheria or tetanus of toxin too small to injure anti-toxin horse serum normal untreated animals –Postulated for the first time that – Described this phenomenon as these hypersensitivity reactions might “hypersensitivity” be the product of immune response –Named these responses “allergic” from the Greek allos ergos, altered reactivity. All historical photos from Silverstein, AM. 1989. A History of Immunology. Academic Press, San Diego Timeline Definitions •1902 - Charles Richet and Paul Portier •Hypersensitivity: –Set sail on the yacht of the Prince of –Broadest (Abbas) - Disorders caused by immune responses Monacco to study the effects of -Dysregulated response to foreign antigen marine toxins in mammals ‣ ‣-Failure of tolerance to self-antigen –Attempted to protect dogs from the effects of toxins by innoculating them –Practical - Used clinically to refer to aberrant or excessive at low doses immune responses generated against foreign antigens, although the same immune processes apply in many autoimmune disease –Re-exposure to innocuous doses resulted in a rapid shock and •Allergy: suffocation –Symptoms elicited by encounter with foreign antigen in a –Coined the term “ana-phylaxis” to previously sensitized individual emphasize its antithesis to the familiar “prophylaxis” 1 Manifestations of Hypersensitivity Common to All Types •Symptoms frequently are localized to the anatomical site of antigen exposure: • Products of the adaptive immune system Site of Exposure Syndrome Common Allergens Symptoms – Require at least one exposure for sensitization to occur – Nasal Pruritis Sensitization can be long lived in the absence of re- Allergic Rhinitis Rhinorrhea exposure (>10 years) due to immunologic memory Congestion Respiratory Mucosa Bronchospasm Asthma Chronic Airway Inflammation Cramping Vomit/Diarrhea G.I. Mucosa Food Allergy Hives Anaphylaxis Manifestations of Hypersensitivity Type I (Immediate) Hypersensitivity • Antigens: Site of Exposure Syndrome Common Allergens Symptoms – Classically exogenous, as opposed to “self” (autoimmune) – Contact via mucous membranes and at low dose appears Contact Hives Urticaria Pruritis to favor type I sensitization Skin • Reactions: – Occur within seconds-minutes of exposure Contact Rash Dermatitis Pruritis – Severity ranges from irritating to fatal • Immune Effect Hives/Edema Abd. Cramping – Blood Systemic Allergy Initial antigen contact leads to IgE production Bronchospasm Hypotension – On re-exposure, antigen-specific IgE initiates the reaction Hypersensitivity: Gell & Coombs Classification IgE Production •Occurs as part of a secondary immune response (generally multiple or persistent exposures) •Class switch to IgE is directed by IL-4 and IL-13 (Th2 cytokines), and requires T cell help (CD40L) •The propensity to make an IgE response to environmental antigens varies among individuals •“Atopic” individuals are those genetically predisposed to form IgE responses. That is, atopy is heritable Immunobiology (Janeway), 6th Ed. 2 Genetics of Atopy Allergy: Sensitization Phase •Complex, multigenic heritability. Candidate genes: • Serum IgE produced by plasma cells has a short –Chrom. 11q - β-subunit of the high affinity FcεRI Τ1/2 (serum Τ1/2 IgG≈30 days; for IgE≈2 days) –Chrom. 5q - Cytokine cluster: IL-3, IL-4, IL-5, IL-9, IL-13 • Rapidly taken up by FcεRI on tissue mast cells –TIM (T-cell, Ig domain, Mucin domain) - surface and circulating basophils –protein, variation assoc. with IL-4/IL-13 prod. –IL-12 p40 subunit (assoc. with asthma and AD) IgE •Variation in IgE response to specific allergens is associated with MHC II genetics –DRB1*1501 is associated with IgE responses to specific ragweed pollen proteins Allergy Epidemic Allergy: Effector Phase •Type I Hypersensitivity diseases, including asthma and •Early Phase Response: within seconds-minutes allergic rhinitis, have been increasing in prevalence in –IgE crosslinking by antigen ¿ release of preformed mediators the economically “advantaged” parts of the world for 30 years –histamine ¿ smooth muscle constriction, mucous secretion, ↑vascular permeability, ↑GI motility, sens. nerve stimulation –The “hygiene hypothesis” attributes increased allergic disease rates to generally decreasing microbial exposure in early life which would normally provide a Th1-promoting effect Allergen IgE ‣-Neonatal bias: ↓IL-12 (DC) and ↓IFN-γ (T cells) ‣-Birth order: ↓allergy rates among 3rd- and 4th-born children ‣-Protective effect of day care ‣-1990 - East/West Berlin immediately after the wall fell: East had ‣-↓vaccination rates, ↑prev. childhood infection, but ↓’ed asthma ‣-Hx of measles or HAV infection, or +PPD ¿↓allergy rates Allergy Epidemic Allergy: Effector Phase •Weighing against the Hygiene Hypothesis: •Early Phase Response: within seconds-minutes –Despite this epidemiologic data, some evidence is hard to –IgE crosslinking by antigen ¿ release of preformed mediators reconcile –histamine ¿ smooth muscle constriction, mucous secretion, ↑vascular ‣-Previous infection with helminths, which generates a strong Th2 permeability, ↑GI motility, sens. nerve stimulation response, is also associated with protection against allergy ‣-Early life exposure to pathogens is also associated with decreased Allergen risk of autoimmune disease (e.g., type I diabetes), a classic Th1- mediated condition IgE –Revised hygiene hypothesis - early life exposure to microbial pathogens influences the balance of immune responsive vs. immune modulating influences 3 Allergy: Effector Phase FcεRI Signaling •Structure: •Early Phase Response: within seconds-minutes –Alpha, Beta, Gamma-Gamma –IgE crosslinking by antigen ¿ release of preformed mediators •Alpha - binds IgE monomer –histamine ¿ smooth muscle constriction, mucous secretion, ↑vascular •Beta, Gamma - signal permeability, ↑GI motility, sens. nerve stimulation •ITAM’s Allergen –Conserved sequences within the IgE receptor tail containing tyrosines –ITAM Tyr is phosphorylated on ligand binding Immediate –Serve as docking sites for downstream Histamine Proteases Hours activating kinases Heparin Minutes Cytokines: Prostaglandins IL-4, IL-13 Leukotrienes Allergy: Effector Phase Eosinophils • Innate responder cell in Type I hypersensitivity •Late Phase Response: 6-24 hours after exposure – Production in marrow induced by IL-3, IL-5, GM-CSF –Mast cell production of newly synthesized mediators – Chemotax to tissue sites: IL-5, Eotaxin-1, 2, 3 ‣-Leukotrienes ¿ smooth mm. contraction, vasodil., chemotaxis ‣-Cytokines ¿ recruitment of PMN and eosinophils – “Primed” by IL-5, eotaxins, C5a ‣ -↑FcγR and C’ receptor expression ‣ -induce FcεR expression Allergen ‣ -↓threshold for degranulation IgE – On activation, eosinophils secrete ‣ -Toxic proteins- major basic protein, eos. cationic ‣ -protein, eos. derived neurotoxin Immediate Histamine ‣ -IL-3, IL-5, GM-CSF, IL-8 Proteases Hours Heparin Minutes Cytokines: ‣ -LT’s Prostaglandins IL-4, IL-13 Leukotrienes Evolutionary Role of Type I Mast Cell Degranulation Response Pre-exposure to Ag Post-exposure to Ag • Mast cells line all subepithelial mucosa – Rapid recruitment of PMN, eosinophils, monocytes to sites of pathogen entry – ↑Lymph flow from peripheral sites to lymph node – ↑G.I. motility ¿ favors expulsion of G.I. pathogens • Important role in parasite clearance –/– – c-kit mice have no mast cells ¿↑susceptibility to trichinella, strongyloides – Eosinophil depletion (Ab-mediated) ¿↑severity of schistosomal infection 4 Evolutionary Role of Type I Anaphylaxis Response •STAT6: •Response to systemic circulation of allergen –Mediates IL-4/IL-13 signaling –Triggering of mast cells in peri-vascular tissue –Required for IgE class switch –Circulating histamine, PG’s/LT’s ¿ vascular leak, vasodilatation –STAT6–/– mice have no IgE –High-output shock (increased cardiac output, ↓↓BP) •Wild type or STAT6–/– mice –Other symptoms: urticaria, flushing, wheeze, laryngeal edema with were injected with 500 N. airway compromise, G.I. cramping, diarrhea brasiliensis larvae •Rapid progression over seconds-minutes •Treatment - •Worm counts and fecal egg counts were assessed at 13 –early administration epinephrine I.M., followed by antihistamines (H1 and H2 blockade) ¿ treat early phase days –subsequent administration corticosteroids¿prevent late phase Urban, et al. (1998) Immunity. 8:255 Type II Hypersensitivity: Type I Sensitivity in Allergy Antibody (Ab) Mediated • Target-specific IgM and IgG mediate damage •Type I Hypersensitivity mediates: • Targets: – Allergic Rhinitis/conjunctivitis (Hayfever) – Self-molecules altered by foreign antigen ¿ neo-epitope – Asthma ‣ -penicillin conjugates to RBC surface proteins ¿ new – Food/Medication reactions penicilloated-protein serves as a target for IgM/IgG ¿ – Contact urticaria intravascular hemolysis – Some forms of eczema – Self-molecules unaltered = breaking of